Spatially Controlled 3D Printing of Dual-Curing Urethane Elastomers

3D printing of functional materials with spatial control of structure and composition is useful for many applications and increases design space. Here, a microextrusion-based method, known as direct ink writing (DIW), is harnessed to further advance 3D complexity by tuning dual-cure ink formulations via varying fillers and filler concentrations. In these inks, low-molecular-weight minor acrylate components enable printing of complex shapes by rapid UV curing during printing while the major heat-cured urethane components provide elastomeric properties when forming a urethane-grafted acrylate polymer (UGAP). The printing process itself displays exquisite control of structure and composition as well as robustness to inks exhibiting a wide range of yield stresses (between 11.5 and 8042 Pa) while still maintaining necessary shape retention during printing. By incorporating micro- or nanosized solid fillers in the inks, an expansive range of both structural and mechanical properties are achievable. Additionally, by modulating the ratio of resin and solid fillers, various combinations of print-mold and pore-forming steps can be employed to expand the design space. The power and versatility of these process permutations are demonstrated by producing a broad range of complex components with controlled properties and performance for applications such as soft robotics.